Mechanism of Translation

Mechanism of Translation Mechanism of Translation - Start

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C483 Spring 2013. 1. The . first amino acid incorporated into proteins ________. . A) can be any of the 20 standard amino acids . B) is an N-. formylmethionine. in E. coli and methionine in other organisms . ID: 273555 Download Presentation

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Mechanism of Translation




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Slide1

Mechanism of Translation

C483 Spring 2013

Slide2

1. The

first amino acid incorporated into proteins ________.

A) can be any of the 20 standard amino acids

B) is an N-

formylmethionine

in E. coli and methionine in other organisms

C) is always

inosinate

D) is an

amidated

methionine residue that is cleaved following termination of translation

2. How

many GTP are hydrolyzed for every

aminoacyl-tRNA

that is successfully inserted into the A site of the ribosome?

A) zero

B) 1

C) 2

D) 4

3.

At the end of the initiation step, the ribosome has a vacant

A) A site.

B) P site.

C) mRNA site.

D)

tRNA

.

E) All of the above.

Slide3

4. How

are the termination codons different from other codons?

A) They contain

thymines

.

B) The termination codon always codes for methionine.

C) They are not recognized by any

tRNA

molecules.

D) Their conformations do not allow them to fit properly in the A site of the ribosome.

5. In translation, GTP hydrolysis is used do all of these except

Position the initial

aminoacyl-tRNA

in the ribosome

Catalyze peptide bond formation

Position incoming

aminoacyl-tRNAs

into the ribosome for elongation

Provide energy for translocation of the ribosome to the next codon.

Slide4

Translation in Prokaryotes

Polyribosome complex with growing mRNANot possible with eukaryotesTranscription in nucleus; translation in cytosolPost-transcriptional modification

Slide5

Initiation

Starts with AUG—formyl-met in bacteriaEstablish reading frameEukaryotes—generally first AUGProkaryotes—Shine-Dalgarno sequence

Slide6

Role of Initiation Factors

Control of assemblyCorrect reading frameCost of 1 GTP

Slide7

Elongation

Initiator

tRNA

in the P-site

Three step mechanism

Position incoming

aminoacyl

-

tRNA

in the A-site

Catalysis of peptide bond formation

Translocation of ribosome

Slide8

Step 1: Position incoming aa-tRNA

Slide9

Step 2: Peptidyl Transferase

Thermodynamically favorable breaking of high energy esterGrowing peptide ends up on tRNA in the A-site

Slide10

Step 3: Translocation

Which moves? Depends on frame of referenceEmpty tRNA in E-site (exit site)Growing polypeptide in P-site A-site is left open with a new codonElongation factor helps at the cost of 1 GTP

Slide11

Termination

Stop codons (UGA, UAG, UAA) end up in A-site

N

ot recognized by

tRNA

; translation stalls

Termination factor binds

Hydrolysis of polypeptide from the

tRNA

; release of protein

GTP bound to termination factor is hydrolyzed

Slide12

Energetic Cost of Translation

Activation of

aminoacyl-tRNA

: 2 ATP equiv.

Initiation: 1 GTP

Elongation step 1: 1GTP

Elongation step 3: 1 GTP

Termination: 1 GTP

Slide13

Example for a 10 AA peptide

Aminoacyl-tRNA

synthesis: 20 ATP

equiv

Initiation: 1 GTP

Elongation positioning: 9 GTP

Elongation translocation: 9 GTP

Termiantion

: 1 GTP

Total: 40 ATP equivalents

Slide14

Answers

B

B

A

C

B


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